Throttle body fuel injection system with improved fuel distribution and idle air control

ABSTRACT

A throttle body fuel injection system and method that is arranged to easily replace four-barrel carburetors includes a throttle body assembly with four main bores, each with a throttle plate and an associated fuel injector. Each injector feeds fuel into a circular fuel distribution ring via a fuel injection conduit, which introduces pressurized fuel into the air stream. The fuel distribution rings and bores have profiles that avoid constrictions for to prevent low pressure zones according to the Venturi effect. The throttle body includes an idle air control circuit having a port opening into main intake bores downstream of the point of fuel distribution into the air stream, thereby reducing the tendency for a lean fuel mixture at idle. An ECU “feed forward” algorithm controls fuel injection as a function of the position of the idle air control valve.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.13/470,121, filed May 11, 2012, and a Continuation of U.S. patentapplication Ser. No. 13/469,938, filed May 11, 2012, issuing as U.S.Pat. No. 9,303,578 on Apr. 5, 2016, the disclosures of which are herebyincorporated by reference as if restated in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to fuel injection systems for internalcombustion engines, and in particular to single point throttle body fuelinjection systems designed for retrofitting vintage carburetion fueldelivery systems.

2. Background Art

A carburetion fuel delivery system uses a carburetor to supply and meterthe mixture of fuel and air in relation to the speed and load of theengine. FIG. 1 illustrates a typical carburetor (10). Carburetor (10)includes one or more barrels (12). A butterfly-type throttle valve (18)is located near the bottom of the barrel (12), the opening and closingof which is controlled through a throttle linkage (not illustrated).Each barrel (12) includes a primary venturi (14) and an annular boostventuri (16), although additional venturis may be used to permit moreprecise metering of fuel and air under different conditions. Liquid fuel(20) is contained in a float bowl (22) and is in fluid communicationwith one or more orifices (21) located at the throat within the annularventuri (16). A jet (24) having a selectively sized port formedtherethrough is disposed within the float bowl (22) at the entrance tothe fluid passage (25) between the float bowl and the venturi (16). Asair flows through the barrel (12) during operation of the engine(depicted using single-headed arrows), a low pressure develops at thethroats of the venturis (14, 16) according to Bernoulli's law. Thedifference in pressure at the fuel across fluid passage (25) causes fuelto flow into the air stream (depicted using double-headed arrows).Orifices (21) atomize the liquid fuel, and because of the low pressurecreated by venturis (14, 16), the fuel is nearly instantaneouslyvaporized. The size of jet (24) determines the air/fuel ratio.

Variations in atmospheric temperature and pressure, engine temperature,load and speed make perfect carburetion nearly impossible to obtainunder all driving conditions. A cold engine, an engine at idle, and anengine at wide-open throttle all require a rich fuel-air mixture, whilea warm engine at cruise requires a lean fuel-air mixture. The airflowalso varies greatly; the airflow through the carburetor at wide-openthrottle may be 100 times greater than the airflow at idle. Complicatingmatters is the fact that gasoline has components with widely varyingboiling points, which may result in less than fully vaporized fuelentering the engine cylinders under certain conditions, particularlywhen the intake manifold is cold.

In contrast, fuel injection systems meter fuel much more precisely thancarburetors, thereby allowing optimal fuel-air mixture to be moreconsistently delivered across the full spectrum of driving conditions.Fuel injection provides increased horsepower, higher torque, improvedfuel economy, quicker cold starting, and other benefits. As a result,fuel injection systems have largely replaced carburetion fuel deliverysystems in automobiles manufactured after 1985.

Fuel injection systems use one or more fuel injectors, which areelectromechanical devices that meter and atomize fuel. In each injector,application of an electrical current to a coil lifts a spring-loadedneedle within a pintle valve off its seat, thereby allowing fuel underpressure to be sprayed through an injector nozzle to form a cone patternof atomized fuel.

Fuel injection systems may be classified as single point, multi-point,or direct injection. As illustrated in FIG. 2, single point injection,also known as throttle body injection, uses one or more fuel injectors(64) located generally in a single location—the throttle body (62). Fuelis sprayed into throttle body (62) for delivery to the cylinders via theintake manifold (not illustrated). Fuel injectors (64) may be of thecontinuous injection variety, for which fuel is sprayed continuously andfuel delivery is controlled by adjusting fuel pressure, or of theintermittent injection variety, for which the injectors are rapidlycycled on and off and fuel delivery is controlled by the duration of the“on” pulse within a cycle. The latter variety is preferable forelectronic control.

Although mechanical and hydraulic control systems are also known in theart, electronic control is the most common manner for governing the rateof fuel injection. A microprocessor- or microcontroller-based computersystem is included within an engine control unit (ECU). The computercontrols various engine and automotive systems as preprogrammedfunctions of numerous signals received from various sensors.

For control of fuel injection, the computer generates periodic pulsesignals for each of the injectors, with “on” pulses for firing the fuelinjectors. One or more driver circuits, located within the ECU, amplifyand condition the pulse signals to be suitable for use with the fuelinjectors. The cycle wavelength is a function of engine speed, and thepulse widths of the “on” pulses are a function of engine load. Enginespeed is typically determined by a distributor output, a tachometeroutput, or a crankshaft sensor. Engine load is typically determined witheither a mass airflow sensor or a manifold absolute pressure (MAP)sensor.

Based on the engine speed and load input signals, the computer generatesthe fuel injector pulse signals. The fuel injector pulse signals areinitially based on target air-fuel ratio values, which are compensatedfor the volumetric efficiency of the engine at its operating speed andload. Target air-fuel ratios and volumetric efficiency coefficients maybe stored in one or more look-up tables in volatile or non-volatilecomputer memory and are accessed using engine load and speed as inputindices. The use of look-up tables allows for rapid response by the ECUto various vehicle operating conditions without the need for extensivetime-consuming calculations. Controlling the fuel injection directlyfrom the look-up tables is referred to as open-loop control.

However, when the ECU operates in a closed-loop control mode, the actualfuel injector pulse signals may vary from those derived directly fromthe look-up tables based on actual engine operating conditions. Inclosed-loop control, the amount of oxygen present in the exhaust gas ismeasured, which provides an indication of whether the engine is runningtoo rich, too lean, or stoichiometrically. The fuel rate supplied to theengine is corrected by the ECU based on the input from an oxygen sensorso that the actual air-fuel ratio supplied to the engine equals thestored target air-fuel ratio under all conditions. In some ECU systems,one or more look-up tables may be updated based on the correctionsderived during closed-loop control for better open-loop and closed-loopcontrol. Closed-loop control is not used under some conditions, such aswhen the exhaust gas temperature is too cold for the oxygen sensor toprovide reliable data.

There are a number of enthusiasts who operate vintage automobiles, oftenmuscle cars, hotrods, and the like, who would benefit from upgrading theoriginal carburetion fuel delivery systems with fuel injection systems.There is a desire, however, to maintain the traditional clean look,feel, and simplicity of a carburetor mounted atop the intake manifold.Throttle body fuel injection systems are ideal for such applications.Accordingly, a niche market has evolved for kits to adapt existingcarburetors with injection capability or to replace existing carburetorswith bolt-in-place throttle body fuel injection systems. Although suchretrofit products exist, which provide many benefits of fuel injection,there is room for improvement in the way that fuel and air are deliveredand mixed within the throttle body assembly.

For example, FIG. 2 is a perspective view of a throttle body fuelinjection system (60) of prior art for replacing a carburetor, such asthat disclosed by U.S. Pat. No. 7,735,475 issued to Farrell et al. onJun. 15, 2010. A section of the throttle body (62) is broken out toreveal the structure of one of the air intake barrels or bores (72), athrottle valve (78), and the idle air control (IAC) circuit (80). Thefuel injectors (64) are positioned so as to inject the fuel just abovethe throttle valve blades (78). The idle air circuit intake (82) islocated at the top of the throttle body (62), and the outlet (84) islocated at the bottom of the throttle body (62). An idle air controllermotor (86) is connected to an IAC valve assembly (88) so as to allow airflow through the IAC circuit (80).

The Farrell et al. device positions the fuel injectors (64) just abovethe throttle blades (78) “to direct fuel to cover the upper surface ofthe throttle blade to improve fuel atomization.” U.S. Pat. No.7,735,475, col. 3 II. 58-59. Other designs, such as those disclosed byU.S. Pat. No. 5,809,972 issued to Grant on Sep. 22, 1998 or U.S. Pat.No. 4,348,338 issued to Martinez et al. on Sep. 7, 1982, utilizeventuris akin to carburetor annular boost venturis (16) of FIG. 1 tocreate low pressure zones to improve atomization and vaporization ofinjected fuel. However, these designs may not provide optimalatomization and mixture delivery to each engine cylinder. Indeed, theuse of venturis with concomitant low pressure zones in fuel injectionsystems has disadvantages, including imprecise fuel delivery due to thepropensity to draw fuel out of the fuel passages downstream of theinjectors during “off” periods in the fuel injection cycle and a greaterrisk for the accumulation of icing within the throttle body undercertain conditions.

As another example, the Farrell et al. IAC circuit (80) is completelyseparate from the intake barrels (72). As a result, idle air flowingthrough the IAC circuit (80) is not mixed with fuel. For this reason,the mixture tends to be too lean during idle conditions, causing roughunstable idle. Analogously, in ECU systems of prior art, fuel injectionand IAC algorithms are also independent of one another. IAC motorposition is controlled primarily as a function of engine speed, andsometimes, coolant temperature. Additional inputs, such as manifoldabsolute pressure or throttle position, may also be considered to ensurethat the engine is actually in an idle condition prior to actuating theIAC motor. Fuel injector pulsing is controlled primarily as a functionof engine speed, engine load, exhaust oxygen levels, and sometimesmanifold air temperature (for air density compensation), coolanttemperature (i.e., for simulating carburetor choke function) or throttleposition (i.e., for simulating carburetor accelerator pump circuitoperation). Fuel injector pulsing is not a function of IAC motorposition. As the IAC opens when the engine begins to idle, the fueldelivered to the engine, initially based on the open-loop look-uptables, becomes too lean. The ECU compensates for the lean idlecondition during closed-loop control by measuring post-combustion oxygenlevels, but any corrective feedback necessarily lags engine operationunder undesirably lean conditions.

Identification of Objects of the Invention

A primary object of the invention is to provide a fuel injection systemfor internal combustion engines that provides superior performance withoptimal fuel distribution and idle control circuitry.

Another object of the invention is to provide an electronic fuelinjection control system that provides superior performance during idleconditions.

Another object of the invention is to provide a fuel injection systemfor retrofitting carbureted engines that installs easily with minimalexternal connections.

SUMMARY OF THE INVENTION

The objects described above and other advantages and features of theinvention are incorporated in a throttle body fuel injection system andmethod that is designed and arranged to easily replace four-barrelcarburetors. The system preferably includes a throttle body assemblywith four main bores, each with a throttle plate and an associated fuelinjector, left and right fuel rails, and an engine control unit that isintegrated into the side of throttle body. Each injector feeds fuel intoa circular fuel distribution ring via a fuel injection conduit, whichintroduces pressurized fuel into the air stream. Both the main bores andthe fuel distribution rings have profiles that avoid constrictions toprevent low pressure zones according to the Venturi effect. That is, thethrottle body according preferred embodiments of the invention avoidsusing a venturi or the venturi effect to accomplish fuel distribution.Fuel is injected through downward-facing outlets at or near the bottomend of the ring.

In a preferred embodiment, the fuel distribution ring is a two-piecering formed of a ring-shaped insert pressed into a ring-shaped outerhousing. The outer housing is ideally integrally formed with thethrottle body casting and includes one or more radial spokes to connectto the walls of the bore. At least one spoke for each ring includes afuel injection conduit that supplies the ring with fuel from aninjector. The insert includes axial grooves intervaled about itsexterior circumference of insert that are joined by a circumferentialgroove formed about the insert. The grooves are in fluid communicationwith the fuel injection conduit.

The throttle body assembly includes an idle air control circuit thatbypasses throttle blades. The idle air control circuit has an inlet portat the top of the throttle body and an outlet port at the bottom ofthrottle body. A cross-over port joins the idle air control circuit toone or more bores within the throttle body below the fuel distributionring. An idle air control motor is used to throttle the amount of airthat flows through the idle air control bypass circuit by varying thestem of an idle air control valve between open and shut positions. Whenthe idle air control valve is open, an air/fuel mixture is drawn intothe into the intake manifold through the idle air control circuit fromthe region of the throttle body bores downstream of the fuel injectionrings. Because an air fuel mixture rather than air is supplied at idle,the tendency for a lean idle fuel mixture is minimized.

Additionally, a unique engine control unit “feed forward” algorithmcontrols the fuel injection as a function of the position of the idleair control motor so that as the IAC valve is opened, the pulse widthsof the fuel injector signals are increased. This feature allows theinitial open-loop-based fuel mixture supplied by system to be moreaccurate and eliminates rough unstable idle associated with closed-loopcontrol lag times.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in detail hereinafter on the basis of theembodiments represented in the accompanying figures, in which:

FIG. 1 is an axial cross-section of the barrel of a typical carburetorof prior art, showing primary and annular booster venturis for drawingfuel from a float bowl into the air stream;

FIG. 2 is a perspective view of a throttle body fuel injection system ofprior art with a broken-out section to reveal the detail of the idle aircontrol circuit;

FIG. 3 is a perspective view of a throttle body fuel injection systemwith a broken-out section to reveal the detail of an annular fueldistribution ring according to a preferred embodiment of the invention;

FIG. 4 is a side elevation of the throttle body fuel injection system ofFIG. 3;

FIG. 5 is a top plan view exploded diagram of the throttle body fuelinjection system of FIG. 3;

FIG. 6 is a perspective view of the throttle body fuel injection systemof FIG. 3 shown with a larger broken-out section to reveal the detail ofan idle air control arrangement according to a preferred embodiment ofthe invention;

FIG. 7 is a block level schematic diagram of the engine control unit ofthe fuel injection system according to a preferred embodiment of theinvention; and

FIG. 8 is a flowchart diagram of the control system algorithmimplemented by the engine control unit of FIG. 7 according to apreferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

FIGS. 3-5 illustrate a throttle body fuel injection system 100 accordingto a preferred embodiment of the invention. Throttle body fuel injectionsystem 100 is a preferably an electronic fuel injection system that isdesigned and arranged to easily replace four-barrel carburetors.Throttle body 100 is designed to bolt on to any square-bore, four-barrelintake, including the common 4150 and 4160 designs. These intakemanifold configurations are found on numerous engines for muscle carsand hot rods, including small and big block engines manufactured byFord, General Motors, and Mopar. There are also aftermarket intakemanifolds available to convert LS engines.

System 100 includes a throttle body 102 with four main bores 112 (eachwith a throttle plate 118), left and right fuel rails 130, and an enginecontrol unit (ECU) 132 that is integrated into the side of throttle body102 opposite the throttle linkage (134). The fuel is fed into one of thefuel rails 130, which is connected to the opposite fuel rail via apassage 136 formed within the throttle body. The fuel rails 130 providefuel to four fuel injectors 104, which are preferably located above thethrottle plates 118. Ideally, there is one fuel injector 104 per bore112.

Each injector 104 feeds fuel into a circular fuel distribution ring 140via a fuel injection conduit 142. Fuel distribution ring 140 introducespressurized fuel into the air stream. Note that unlike the carburetorannular booster venturis 16 of FIG. 1, fuel distribution rings 140 haveprofiles that do not form constrictions for creating low pressure zonesaccording to the Venturi effect. Indeed, the inner and outer diametersof fuel distribution rings 140 have substantially straight sides forminimal pressure drop. Also unlike the carburetor annular boosterventuris 16 of FIG. 1, in which the fuel is introduced into the airstream through orifices 21 located in the interior side wall of thering, fuel is injected through downward-facing outlets at or near thebottom end of ring 140.

In a preferred embodiment, ring 140 is a two-piece ring formed of aring-shaped insert 141 pressed into a ring-shaped outer housing 143.Outer housing 143 is ideally integrally formed with the throttle bodycasting and includes one or more radial spokes 145 protruding therefromthat connect to the walls of bore 112 for securing outer ring housing143 within bore 112. At least one spoke 145 for each ring 140 includes afuel injection conduit 142 that supplies ring 140 with fuel from aninjector 104. Insert 141 fits within outer housing 143. Insert 141includes axial grooves 144 intervaled about the exterior circumferenceof insert 141. A circumferential groove 146 formed about insert 141fluidly connects axial outlet grooves 144 with fuel injection conduit142, thereby allowing fuel to flow from injector 104 through conduit142, through circumferential groove 146, and through axial grooves 144to discharge downwardly at or near the bottom end of ring 140. Althoughaxial grooves 144 and circumferential groove 146 are shown formed ininsert 141, in an alternative embodiment either the axial grooves, thecircumferential groove, or both, may be formed within the interior ofouter housing 143.

The design of annular injection ring 140 produces an air/fuel chargewith superior mixing for even distribution to the cylinders. Betterair-fuel mixing provides for better idle quality, better starting, andbetter overall drivability throughout the engine rpm range. According toa preferred embodiment of the invention, each injection ring 140includes six axial outlets 144, although a greater or lesser number canbe used as desired. However, it is desirable that the totalcross-sectional area of axial grooves 144 within each injection ring 140be larger than the total cross-sectional area exiting the correspondingfuel injector 104 so as to lower the kinetic energy of the fuel dropletsentering the air stream. In a preferred embodiment, the totalcross-sectional area of axial grooves 144 is approximately fifty percentlarger than the area exiting fuel injector 104.

FIG. 6 illustrates the idle air control (IAC) circuitry 120 of fuelinjection system 100 according to a preferred embodiment of theinvention. Like the IAC circuitry 80 of the prior art throttle body fuelinjection system of FIG. 2, IAC circuitry 120 bypasses throttle blades118, which are shut when the engine is idling (although a closedthrottle still allows a small amount of air to enter the manifold). IACcircuitry 120 is formed with an opening 122 at the top of the throttlebody 102 and an outlet port 124 at the bottom of throttle body 102. Anidle air control motor 126 is used to throttle the amount of air thatflows through the bypass circuit 120 by varying the stem of an IAC valve128 between open and shut positions.

However, unlike the IAC circuitry 80 of the prior art throttle body fuelinjection system of FIG. 2, IAC circuitry 120 includes one or morecrossover inlet ports 121 that open between bores 112 below fuelinjection ring 140 and IAC bypass circuit 120. Accordingly, when IACcircuit 80 is bypassing air around throttle plates 118, an air/fuelmixture is drawn from the region of bores 112 downstream of fuelinjection rings 140 through ports 121 into the intake manifold (ratherthan drawing air only from upstream of the fuel injectors as is done inthe prior art injection system of FIG. 2). By drawing an air fuelmixture into the IAC circuit 80, the propensity for a lean fuel mixturewhile idling is lessened. Opening 122 may be left open or mayalternatively be plugged.

The tendency for a lean idle fuel mixture is also minimized by a uniqueECU algorithm according to a preferred embodiment of the invention. ECU132 (visible in FIG. 5) controls the position of IAC motor 126 as afunction of one or more inputs, which may include engine rpm, engineload, throttle position, and coolant temperature, so that engine rpm atidle is maintained at a constant desired value regardless of engine loador temperature, for example. For instance, when the vehicle is idling ata traffic signal, if the air conditioning compressor is engaged, the IACvalve 128 may need to be nearly fully open in order to maintain desiredengine speed, but if the air conditioning compressor is disengaged, theIAC valve may only need to be open twenty percent.

In prior art control systems, IAC motor position is not an inputvariable used in the determination of fuel injection levels. However, asillustrated in the block level schematic diagram of FIG. 7, ECU 132employs a unique feed-forward algorithm that increases the pulse widthsof the fuel injector signals based on the controlled movement of the IACmotor. This feature allows the initial open-loop-based fuel mixturesupplied by system 100 to be more accurate than the initialopen-loop-based fuel mixture supplied by prior art system 60 andeliminates rough unstable idle associated with the closed-loop lagtimes.

A computer processor 150, such as a microprocessor or microcontroller,is included within ECU 132. The computer processor 150 controls variousengine and automotive systems as preprogrammed functions of numeroussignals received from various sensors. Computer memory 152, which mayinclude both random access memory (RAM) and non-volatile memory such asFlash memory or electrically erasable programmable read-only memory(EEPROM), is in electrical communication with computer processor 150 asis well known to those of ordinary skill in the art of computer systemdesign. Discrete electronic components may be combined in anapplication-specific integrated circuit (ASIC) as appropriate.

As described in greater detail with respect to FIG. 8, processor 150executes an algorithm 160 for controlling the position of IAC motor 126(FIG. 5) so as to maintain actual engine idle speed at specified idletarget speed. Target idle RPM data 162 are stored in memory 152 and mayprovide specified idle target speeds as a function of coolanttemperature, throttle position, air conditioner settings, or similarinputs. Processor 150 receives an engine speed input 154 and whateverother inputs (not illustrated) are appropriate for the particular IACalgorithm 160 that is implemented. Based on IAC algorithm 160, processor150 generates an IAC position output signal 156, which is proportionalto the shaft position of IAC motor 126. IAC position output signal isthereafter formatted and conditioned for actuating IAC motor 126 asappropriate.

Fuel injector pulsing is controlled by algorithm 164 primarily as afunction of engine speed 154 and engine load 158 (e.g., MAP or mass airflow), as is known in the art. Other inputs (not illustrated) includingexhaust oxygen levels, manifold air temperature, coolant temperature,and throttle position, may be used, depending on the control systemtopology. According to a preferred embodiment of the invention, fuelpulse algorithm 164 is unique in that it includes the IAC positionoutput signal 156 as an input. Accordingly, processor 150 generates afuel pulse width output signal 157 that in open-loop control immediatelyincreases the fuel pulse width output signal 157 as the IAC valve 128(FIG. 6) is opened without the lag time associated with closed-loopcontrol based on oxygen sensor readings. The fuel pulse width outputsignal 157 is thereafter formatted and conditioned for actuating fuelinjectors 104 (FIG. 6) as appropriate.

FIG. 8 is a flowchart diagram of the open-loop control system algorithmimplemented by ECU 132 according to a preferred embodiment of theinvention. Target idle speed data 162, volumetric efficiency data 170,and target air/fuel ratio data 172 are stored in memory 152 of ECU 132(FIG. 7). According to IAC algorithm 160 (FIG. 7), the appropriatetarget idle rpm value from target idle speed data 162 is summed with thenegative feedback of the actual engine rpm value 154, the result ofwhich comprises the input to a proportional-integral-derivative (PID)controller algorithm 174. As PID controllers are well known in the art,no further details are provided herein. However, controller topologiesother than PID may be used as appropriate. The output of PID controller174 is a signal 156 that is proportional to the position of IAC motor126 (FIG. 6). IAC position signal 156 is converted by an IAC motordriver circuit 176 into an appropriate signal that actuates IAC motor126.

An airflow estimator algorithm 178 determines the mass air flow rateinto the engine from engine speed 154 and manifold absolute pressure 158based on the engine's volumetric efficiency factors 170. Other inputs(not illustrated), such as induction air temperature in the engine'sintake manifold and barometric pressure may be used to more accuratelydetermine mass air flow, as is known to routineers of ordinary skill inthe art. Next, a fuel pulse width calculation algorithm 184 calculatesfrom the mass air flow rate signal 180 and the target air/fuel ratiotable 172 the fuel injection pulse width 182 required to add therequired fuel mass to achieve the target air/fuel ratio for that enginespeed and load.

According to a preferred embodiment of the invention, a “feed forward”signal 184 that is proportional to IAC position signal 156 is summedwith the initial fuel injection pulse width signal 182 so as to add morefuel as the IAC valve 128 (FIG. 6) is opened. The combined fuelinjection pulse width signal 186 is converted into a period waveformhaving a frequency based on the engine rpm signal 154 with suitableelectrical characteristics to actuate fuel injectors 104 (FIG. 6) byinjector driver circuitry 188.

The Abstract of the disclosure is written solely for providing theUnited States Patent and Trademark Office and the public at large with away by which to determine quickly from a cursory reading the nature andgist of the technical disclosure, and it represents solely a preferredembodiment and is not indicative of the nature of the invention as awhole.

While some embodiments of the invention have been illustrated in detail,the invention is not limited to the embodiments shown; modifications andadaptations of the above embodiment may occur to those skilled in theart. Such modifications and adaptations are in the spirit and scope ofthe invention as set forth herein:

What is claimed is:
 1. A fuel injection system (100) comprising: athrottle body assembly (102) defining an outlet side dimensioned tomount atop an intake manifold of an internal combustion engine; a bore(112) formed through said throttle body assembly, said bore defining aninlet and an outlet wherein said outlet is open at said outlet side; athrottle valve (118) disposed in said bore; a fuel injector (104)mounted to said throttle body assembly; a fuel distribution ring (140)disposed in said bore, said ring defining upper and lower ends and acircular wall with inner and outer circumferences therebetween; aplurality of openings (144) formed in said lower end of said fueldistribution ring in fluid communication with said fuel injector wherebyfuel is injectable from said fuel injector into said bore through saidplurality of openings at a first point upstream of said throttle valve;and an idle air control passage (120) formed through said throttle bodydefining an outlet port (124) in fluid communication with said bore atsaid outlet side whereby said throttle valve is bypassed by an air/fuelmixture entering the idle air control passage through an inlet port(121) in fluid communication with said bore at a second point that isdownstream of said first point and upstream of said throttle valve. 2.The fuel injection system of claim 1 wherein said fuel distribution ringis substantially coaxial with said bore, and said circular wall of saidfuel distribution ring is substantially straight.
 3. The fuel injectionsystem of claim 2 wherein said fuel distribution ring includes an outergenerally ring-shaped housing (143) and a ring-shaped insert (141)disposed within said housing, said housing defining an innercircumference and said insert defining an outer circumference.
 4. Thefuel injection system of claim 4 wherein said plurality of openings aredefined by a plurality of axial grooves (144) formed in at least one ofthe group consisting of: the outer circumference of said insert; and theinner circumference of said outer housing; and wherein said fueldistribution ring further comprises a circumferential groove (146)formed in at least one of the group consisting of: the outercircumference of said insert; and the inner circumference of said outerhousing, said circumferential groove fluidly connecting said pluralityof axial grooves with a conduit (142) fluidly coupling said plurality ofoutlets to said fuel injector.
 5. A fuel injection system (100)comprising: a throttle body assembly (102) defining an outlet sidedimensioned to mount atop an intake manifold of an internal combustionengine; a bore (112) formed through said throttle body assembly, saidbore defining an inlet and an outlet wherein said outlet is open at saidoutlet side; a throttle valve (118) disposed in said bore; a fuelinjector (104) mounted to said throttle body assembly; a fueldistribution ring (140) disposed in said bore, said ring defining upperand lower ends and a circular wall with inner and outer circumferencestherebetween; a plurality of openings (144) formed in said lower end ofsaid fuel distribution ring in fluid communication with said fuelinjector whereby fuel is injectable from said fuel injector into saidbore through said plurality of openings at a first point upstream ofsaid throttle valve; an idle air control passage (120) formed throughsaid throttle body defining an outlet port (124) in fluid communicationwith said bore at said outlet side and an inlet port (121) in fluidcommunication with said bore at a second point that is downstream ofsaid first point and upstream of said throttle valve; and an idle aircontrol valve (128) disposed within said idle air control passage. 6.The fuel injection system of claim 5 wherein said fuel distribution ringis substantially coaxial with said bore.
 7. The fuel injection system ofclaim 5 wherein said circular wall of said fuel distribution ring issubstantially straight.
 8. The fuel injection system of claim 5 whereinsaid fuel distribution ring includes an outer generally ring-shapedhousing (143) and a ring-shaped insert (141) disposed within saidhousing, said housing defining an inner circumference and said insertdefining an outer circumference.
 9. The fuel injection system of claim 8further comprising: a conduit (142) fluidly coupling said plurality ofoutlets to said fuel injector; wherein said throttle body assemblyincludes a throttle body casting; and said outer housing of said fueldistribution ring and said conduit are integral with said throttle bodycasting.
 10. The fuel injection system of claim 8 wherein said pluralityof openings are defined by a plurality of axial grooves (144) formed inat least one of the group consisting of: the outer circumference of saidinsert; and the inner circumference of said outer housing.
 11. The fuelinjection system of claim 10 further comprising: a circumferentialgroove (146) formed in at least one of the group consisting of: theouter circumference of said insert; and the inner circumference of saidouter housing, said circumferential groove fluidly connecting saidplurality of axial grooves with said conduit.
 12. The fuel injectionsystem of claim 5 wherein a diameter of said bore is substantiallyconstant from said inlet to said outlet so as to minimize any Venturieffect within said bore.
 13. The fuel injection system of claim 5wherein said inner diameter of said fuel distribution ring issubstantially constant from said upper end to said lower end so as tominimize any Venturi effect within said fuel distribution ring.
 14. Thefuel injection system of claim 5 wherein said plurality of openings facetoward said outlet of said bore.
 15. The fuel injection system of claim5 wherein a total area of said plurality of openings is greater than adischarge area of said fuel injector.
 16. The fuel injection system ofclaim 5 wherein said idle air control passage defines an opening (122)at a top of the throttle body opposite said outlet side.
 17. The fuelinjection system of claim 5 further comprising: a controller (132)operatively coupled to said fuel injector and arranged for increasing anamount of fuel injected by said fuel injector as a function of aposition of said idle air control valve.
 18. The fuel injection systemof claim 17 wherein said controller includes driver circuitry (188) forcreating a periodic pulse signal to actuate said fuel injector, and saidcontroller includes a first algorithm for determining a pulse width(186) of said periodic pulse signal as a function of the sum of a firstvalue (182) that is representative of an initial pulse width and asecond value (184) that is representative of a position of said idle aircontrol valve.
 19. The fuel injection system of claim 18 wherein saidcontroller includes a second algorithm for determining said first valuefrom a third value (180) that is representative of an air flow into saidinternal combustion engine and a fourth value (172) that isrepresentative of a target air/fuel ratio.
 20. The fuel injection systemof claim 19 wherein said controller includes a third algorithm fordetermining said third value from a fifth value (154) that isrepresentative of a rotational speed of said internal combustion engine,a sixth value (158) that is representative of a load imposed on saidinternal combustion engine, and a seventh value (170) that isrepresentative of a volumetric efficiency of said internal combustionengine.